The present invention relates to a magnetic head which is mounted on a magnetic recording/playback device such as a video tape recorder, a floppy disc drive device, or a hard disc drive device, etc.
In a so-called composite type magnetic head in which an oxide material such as Mn-Zn ferrite or ceramics and a magnetic thin metal film are made in composite fashion, a junction or bonding of the oxide material with the magnetic thin metal film may be required in the manufacturing process thereof. For example, in a magnetic head in which the magnetic thin metal film is made composite in a direction perpendicular to a gap portion, it is necessary to bond another oxide substrate to an oxide substrate on which a magnetic thin metal film is formed so that both the substrates sandwich the magnetic thin metal film therebetween. Alternatively, an oxide substrate is bonded to both sides of a magnetic thin metal film which is made into a thin strip.
Fusion glass having a high melting point is used for carrying out the above mentioned bonding of an oxide substrate and a magnetic thin metal film, unless a problem occurs. This is because the high melting point glass has advantages that such glass can be washed with organic solvent since it is chemically stable and strong bonding can be obtained.
However, it is necessary to elevate the fusing temperature not less than 550.degree. C. for carrying out bonding with glass having a high melting point. Accordingly, distortion due to thermal expansion may be caused in ferrite or magnetic thin metal film and the influence by the distortion may induce cracking in a magnetic core, resulting in deterioration of magnetic characteristics.
When the magnetic thin metal film is formed of a ferromagnetic amorphous metallic alloy, a so-called amorphous alloy, the fusing temperature is generally not less than the crystallization temperature (crystallization temperature is generally 400.degree. C. to 500.degree. C.). Accordingly, crystallization of the amorphous alloy deteriorates soft magnetic characteristics. If the oxide substrate is bonded to the magnetic thin metal film with a high melting point glass, the glass and the magnetic thin metal film, or the oxide substrate and the magnetic thin metal film, effect an oxidation-reduction reaction at the interface therebetween so that a region at which the permeability is remarkably lowered results, that is, a reaction layer may be formed.
If the above mentioned problems occur, a low temperature bonding agent such as a fusing glass having a low melting point, water glass or organic adhesive agent is used to bond the oxide substrate to the magnetic thin metal film. However, if the above mentioned low temperature bonding agent is used for bonding the oxide magnetic material to the magnetic thin metal film, the low temperature bonding agent has a disadvantage that it is inferior to the high melting point glass in bonding strength, weather resistance, wear resistance, surface characteristics and precision of thickness of the bonding layer.
On the other hand, it is said that bonding with high melting point glass which is chemically stable and high in bonding strength as is similar to bonding between the oxide substrate and the magnetic thin metal film in the above mentioned composite type magnetic head is preferable to bond the magnetic cores themselves at a gap therebetween in a magnetic head formed of oxide magnetic material such as Mn-Zn ferrite or a magnetic head in which the oxide magnetic material and the magnetic thin metal film are made composite. Particularly, this tendency is strong in a magnetic head which is mounted on a magnetic recording/playback device such as a video tape recorder since such a magnetic head requires durability.
However, if magnetic cores in which the oxide magnetic material such as ferrite is made composite, the magnetic thin metal films are bonded with each other with glass, and a reaction layer may be formed. If the interface between the ferrite and the magnetic thin metal film is formed in parallel with a magnetic gap, the reaction layer acts as a false gap, resulting in waves in frequency characteristics of the playback output.
If glass having a melting temperature not higher than 500.degree. C. is used in order to avoid the false gap, reliability is low in humidity resistance and hardness. Low melting point glass having a low reliability should be used as a secondary fusion glass, particularly for a composite type magnetic head (in which integrated magnetic cores are embedded in a non-magnetic member, a so-called slider by glass fusing) which is mounted on a floppy disc drive device or a hard disc drive device, which requires glass bonding several times. That is, such a type of magnetic head is produced by first conducting a gap bonding (first fusing) with high melting point glass and thereafter by fusing (second fusing) the bonded and integrated magnetic cores to the slider with a low melting point glass to be embedded for fixing the cores on the slider. Accordingly, if the first fusing glass is melted out on the second fusing so that the gap length of track width, etc. changes, the reliability of the magnetic head would be largely lowered. Therefore, only low melting point glass can be used as the second fusing glass.
In such a manner, it is difficult for a gap bonding method using fusing glass to achieve, while keeping the magnetic characteristics inherent to the magnetic core, a prevention of false gap formation and bonding strength of the magnetic head which requires bonding of two or more films of glass.
A magnetic head in which Au is mainly used as the material in lieu of fusing glass, and wherein Au films are bonded with each other by thermal diffusion at a low temperature for gap bonding, is disclosed by IEEE TRANSACTIONS ON MAGNETICS, Vol. 24, No. 2, Mar. 1, 1988. The magnetic head is produced by successively laminating SiO.sub.2, Mo and Au on the abutting faces of a pair of magnetic cores to a given film thickness and abutting to bond Au film to themselves by thermal diffusion.
Since thermal diffusion with Au is conducted at a temperature very much lower than a fusing temperature for glass bonding, it is said that there is no influence by distortion due to thermal expansion, and a false gap will never be formed, and deterioration of head characteristics caused by crystallization can be prevented.
Although the method of bonding a gap which mainly uses Au as a gap material to bond the Au layers themselves by thermal diffusion at a low temperature can solve the prior art problem to some extent by using fusing glass, the bonding strength between an Au layer and the oxide material or an Au layer and the magnetic thin metal film is insufficient, so that it is not enough for a magnetic head mounted on a magnetic recording/playback device such as a video tape recorder which requires a high durability for the magnetic head.
If glass fusing using high melting point glass is adopted for bonding between a magnetic thin metal film and an oxide substrate or magnetic cores themselves at a gap therebetween in a composite type magnetic head as mentioned above, problems such as deterioration of the magnetic characteristics of magnetic thin metal film and the false gap generation due to formation of a reaction layer would occur. On the other hand, it is difficult to assure sufficient bonding strength by bonding using low melting point glass or an organic adhesive agent and the like, and a problem remains in reliability. Although a method of gap bonding by thermal diffusion of Au layers has been proposed, the bonding strength is not sufficient.
In such a manner, it is a fact that it is difficult in the prior art to assure both magnetic characteristics and bonding strength.
Accordingly, the present invention was proposed in view of these prior art circumstances.